DE 10 2004 014 547 A1, DE 10 2005 031 957 A1, DE 10 2005 054 122 A1 and EP 1 190 855 A1 each disclose inspection systems for printing presses.
DE 10 2004 061 951 A1 discloses a system for controlling the quality of printed materials, in particular printed sheets, having a device for recording image data for the printed materials that are moved through a sheet-processing machine, for example a sheet-fed printing press, an analysis device downstream of the recording device for processing the image data in conjunction with data that are stored in a memory linked to the analysis device, wherein the recording device is capable of scanning printed material that reflects the fields to be inspected, and the analysis device is capable of determining therefrom the data that characterize the fields to be inspected or the image content thereof, storing these in the memory, and evaluating them during the subsequent analysis of image data for printed materials that are or will be processed, wherein it is provided that in the analysis device, using corresponding specifications regarding threshold values for brightness and/or color tone and/or saturation, those image regions that are a special color and are to be inspected are separated from image regions that will not be inspected.
EP 0 749 833 A2 discloses a video-based color sensor array for the control system of a printing press and a method for using the same, wherein for the joint inspection of a printed sheet, both a color camera for measuring in the visible range of the electromagnetic spectrum and a black and white camera for measuring in the non-visible infrared range are provided.
DE 10 2005 018 855 A1 discloses a device for inspecting, in particular, printed products produced by a printing press, in which a first camera, e.g. having a standard lens is provided, which is directed toward an inspection field on the printed product to be inspected, and at least one additional camera, e.g. having a telephoto lens is provided, which is directed at least partially toward the same inspection field already being monitored by the first camera, wherein the first camera captures an overview image of an inspection field, and the second camera captures a detail image of the inspection field with higher spatial resolution.
U.S. Pat. No. 5,912,988 A discloses a method for analyzing images, in which an overall image is divided into multiple individual fields, wherein each field can be evaluated individually.
In the production of printed products in a production system that has a printing press, it is customary for the printing properties of these printed products to be inspected in particular continuously, but at least sporadically, i.e. on a random basis, during the production process used to produce these printed products, in order to ensure the highest possible production quality. The properties of said printed product to be inspected that influence overall production quality include, e.g. the color density and/or the color value and/or the sharpness, in particular the edge sharpness of a printed image applied to a printing substrate. To carry out these inspections, inspection systems frequently are used which are preferably equipped with at least one optoelectronic camera, wherein said camera photographically images at least a portion of at least one printed image of the printed product in question, and from said imaging preferably generates digital image data of the image, which are then made available to an analysis unit, in particular an electronic analysis unit. The analysis unit analyzes the obtained image data with regard to the properties of said printed product to be inspected, and typically assesses the results of said inspection in that the analysis unit signals, dependent upon said inspection result, whether or not the inspected copy of the printed product meets the necessary requirements for production quality, e.g. established in advance by way of boundary values. Where necessary, when a production quality deficit is detected, the analysis unit transmits at least one signal, e.g. a control signal, to a unit of the production system or printing press involved in the production process, in order to correct this deficit in subsequently produced printed products and/or to channel defective printed products out of the production flow.
In security printing in particular, i.e. in the production of banknotes and other security documents, but also in the production, e.g. of high-quality packaging, a number of different printing methods are used in the production process. For example, an intaglio printing method and/or an offset printing method and/or a screen printing method and/or a plateless printing method, i.e. a digital printing method, e.g. an inkjet printing method and/or a laser printing method may be used in the production of banknotes. The various printing methods produce printed images that have different print properties, which is why, when performing an inspection of printed products having printed images produced by different methods, adjustments to the inspection system used for the inspection are necessary. A system is needed for the inspection of printed products produced in a production process using multiple different printing methods, which system is capable of examining at least one of the properties in or on each of the printed images of said printed product that have been printed by different printing methods.